An ion exchange polymer is a kind of synthetic resin, and has a structure for ionization as an ionic group in a part of the molecular structure thereof. The ion exchange polymer performs ion exchange with an ion in a solvent such as water. Behavior thereof is in accordance with selectivity for the ion. The ion exchange polymer is largely classified into a cation exchange polymer and an anion exchange polymer. By using a difference in adsorption between a fixed ion in the polymer and a counter ion (ion to be exchanged) in various solutions, ions contained in the solutions can be separated.
Electric charge characteristics of a biomolecule are determined by various factors such as a charge of the entire molecules, a charge density, a method of distribution of a surface charge, and the pH of a solution. For example, protein contains many kinds of ionic amino acids such weakly acidic and weakly basic amino acids, and has both a positive charge and a negative charge on surface of protein molecule. The sum of the charges is called an effective surface charge, and a charge state of an amino acid depends on the pH. Therefore, an effective surface charge of a protein molecule is changed into positive or negative charge, depending on the pH of a solution.
Ion exchange chromatography is a method of collecting a biomolecule based on reversible binding and eluting the biomolecule with a carrier having an opposite charge, by utilizing such a change of charge state (i.e., effective surface charge) of the biomolecule caused by the pH or a salt concentration (for example, Patent Literatures 1 and 2 and non-Patent Literature 1).
However, when such a collecting operation is performed, a surfactant, a high concentration salt, or the like is used during elution. Therefore, it is difficult to maintain a three-dimensional structure of a target or to collect the target while the target is alive.